Blending of Silicone Rubber
Silicone rubber raw rubber is relatively soft and has certain plasticity. It can be directly mixed by mixer or internal mixer without plasticizing. There are several mixing methods:

(1) Refiner mixing
The optimum speed ratio of rollers in twin-roll mill is (1.2-1.4):1. The higher speed ratio of fast rollers leads to faster mixing, and the lower speed ratio can make the film smooth. The roller must be provided with cooling water and the mixing temperature should be below 40 (?) C to prevent the loss of coke burning or volatilization of vulcanizate. When mixing, the roll spacing is small (1-5 mm), and then increases gradually. Feeding and operation sequence: raw rubber (wrapping roll) - reinforcing filler - structure control agent - heat-resistant additive - colorant - thin pass 5 times - blanking, oven heat treatment - refining - vulcanizing agent - thin pass - parking overnight - refining - sheeting. Rubber can also be treated without oven heat treatment. After adding heat-resistant additives, vulcanizing agent can be thinned through again. It can be put in overnight refining, and then put in refining tablets for several days. The mixing time is 20-40 minutes.

Silicone rubber is wrapped with slow roll (front roll) when it is added to the rubber mixer, and fast roll (back roll) when mixing. It must be able to operate on both sides in rubber mixing. Because the silicone rubber compound is soft, ordinary putty knife can be used in mixing. When thin through, the thin sheet can not be pulled down like ordinary rubber, but scraped with steel, nylon or wear-resistant plastic scraper.

In order to facilitate cleaning and prevent lubricating oil from leaking into rubber, movable rubber sheets should be used. Gas-phase silica is easy to fly and harmful to human body. Corresponding protective measures should be taken. If powder peroxide is used directly in mixing, explosion-proof measures must be taken, and paste peroxide is the best choice.


(2) mixing in internal mixer
When mixing with 2L mixer in laboratory, the mixing time is 6-16 minutes. There is no special difficulty in mixing. When the charging coefficient is 0.74, the mixing can also be carried out normally in a 160mm smelter. The discharging temperature is related to the type of reinforcing filler. When the weak reinforcing filler and precipitation silica are used, the discharging temperature is below 50 and when the fumed silica is used, the discharging temperature is about 70.

(3) Rubber parking and refining
After the mixing of silicone rubber compound, the stopping time should be no less than 24 hours, so that all kinds of compounding agents (especially structural control agents) can fully play a role in the raw rubber. After parking, the rubber hardens and the plastic value decreases. It must be refining before use. Re-smelting uses a smelting machine, starting with a larger roll spacing (3-5mm), when the rubber is hard, the surface is wrinkled, wrapped on the front roll. As the refining time prolongs, the rubber gradually softens, and roll spacing decreases (0.25-0.5mm), and the rubber is quickly wrapped on the back roll. When the rubber becomes soft and the surface is smooth and smooth, the sheet can be discharged. The film surface is wrinkled due to insufficient refining, and the compound sticks to the roll when the refining is excessive. The refining temperature is generally controlled at room temperature.